As methods for joining resin members with each other, a method using an adhesive and a welding method such as hot plate welding, vibration welding, ultrasonic welding and spin welding, have been conventionally known. In recent years, an injection welding method such as DRI and DSI, and a laser welding method have also become available.
The joining method using an adhesive is a manual operation by a worker and this is an inefficient operation. Furthermore, this method is disadvantageous in that stable joining strength cannot be obtained and, depending on the kind of the resin member, a sufficiently high adhesive force may not be obtained. Also, environmental contamination is a problem with this method.
Hot plate welding has problems that the cycle is long, a filling material is necessary, or welding cannot be effected in the water-absorbed state. Vibration welding is disadvantageous in that, for example, the welding part shifts 1 to 2 mm due to the vibration, giving rise to unsuitability for precision components, a flash is generated to cause clogging of a filter or the like, or welding can be hardly effected when a warp exists. Ultrasonic welding has the drawbacks that, for example, the weld strength is low, the airtightness is poor, or the welding is applicable only to small members. Spin welding is applicable only to circular members and has the problems that a filling material is necessary or welding cannot be effected in the water-absorbed state.
Also, DRI and DSI, which are injection welding methods recently employed for intake manifolds, have a problem that despite high weld strength, for example, the die is expensive, the molding machine needs to be modified, and these welding methods cannot be used unless the material has particularly good flowability.
On the other hand, the laser welding is a method of welding a resin member non-absorptive of laser light and a resin member absorptive of laser light by abutting these members against each other, where laser light is irradiated on the joining face from the non-absorptive resin member side, and the absorptive resin member forming the joining face is melted by the energy of laser light, thereby effecting joining (see, for example, Japanese Unexamined Patent Publication (Kokai) No. 60-214931 and Japanese Examined Patent Publication (Kokoku) No. 5-42336).
However, there is a problem that a sufficiently high joining strength cannot be obtained in joining resin members which are dissimilar and, particularly, are resin members which are dissimilar materials having no or little adhesive property, for example, members such as nylon 6 and nylon 12.